Hypertrophic cardiomyopathy (HCM) is a congenital cardiac disease that has been refractory to treatment. Patients are managed symptomatically with many cases progressing to heart failure or Sudden Cardiac Death. One of the main impediments to directed treatment is an incomplete understanding of the transition from mutation to disease morphology and hemodynamics. This project seeks to understand the molecular mechanisms related to muscle regulation that underlie the disease phenotype. The aims of the project are to: 1) Determine among a group of HCM mutations if shifting between actin states is a common method of altering myocardial regulation. Two previously studied disease causing mutants are known to alter this pathway. Once the commonality of altering this regulatory step is shown, therapies can be targeted towards reversing this alteration. With partial activation of actin by NEM-S1, ATPase rates will show an increase if the mutation stabilizes the active state. However at maximal activation, when both mutant and control are fully in the active state, the ATPase rates should be similar. Studies of myosin-ADP binding to actin will determine the functional state of actin. Fluorescent probes will be used to study the movement of tropomyosin and troponin, two key regulatory proteins, in terms of rapid kinetics and equilibrium. 2) Confirm the results of Aim 1 by simulating steady state ATPase activities. Models of regulation are used to explain the transitions along the pathways of the muscle contraction cycle. Comparing binding to ATPase data with models has been problematic due to the difference in ionic strength conditions between the different assays. Using a preparation of the muscle filament that allows ATPase assays to be conducted at higher salt conditions, it will be possible to compare ATPase rates to the binding data. 3) Try to reverse the effects of HCM mutants by combination with phosphorylated troponin which has the opposite effect on actin states. Studying the interaction between HCM mutations and a physiological modification that stabilizes the inactive state will show the effects of a likely therapeutic approach to treating the disease. The key to discovering how a mutation of muscle proteins alters myocardium is to understand its effect on muscle regulation. At the end of this project, this mechanism will be better understood along with potential therapies targeting the specific affected step. These therapies will focus on treating the primary molecular pathology as opposed to the secondary effects of ventricular hypertrophy and outflow obstruction. RELEVANCE: The project will examine the method by which genetic mutations cause the disease state Hypertrophic Cardiomyopathy. This will allow for targeted therapy that alters the specific step affected by the mutations.